1. Field of the Invention
The present invention generally relates to laser machining and, more particularly, to a laser bending method and apparatus for bending a thin metal plate by irradiation of a laser beam.
2. Description of the Related Art
There is known a technology in which a laser beam is irradiated so as to bend a thin metal plate or correct warpage of a thin metal plate. In a conventional laser bending method of a thin metal plate, a laser beam is focused on a surface of a thin metal plate as a work piece (referred to as a just focused state) so as to efficiently bend the thin metal plate.
In the conventional laser bending method, the front side of the thin metal plate is heated to a predetermined temperature by irradiation of a laser beam, but the backside of the thin metal plate is not to be heated. The work piece to be machined is bent by utilizing a phenomenon that the work is self bent due to a difference in stresses generated in the front side and the back side of the work while the heated portion is being cooled. In this case, the work piece is bent in a state in which the front side of the work is a concave surface. That is, the work piece is concave toward the laser beam.
Thus, according to the conventional laser bending method, a difference in temperatures between the front surface and the back surface is generated by quickly heating a front surface of a work piece before a temperature of a back surface of the work piece increases due to irradiation of a laser beam in a just focused state or close to the just focused state. Especially, in a case where irradiation of a laser beam is carried out in a state in which a work piece is placed on a support table such as a jig, a difference in a temperature between the back surface and the front surface in a laser beam irradiated portion of the work since a large amount of heat is released to the jig from the back surface of the work piece (the surface contacting the jig).
According to the above-mentioned conventional laser bending method, it has been thought that a work piece such as a thin metal plate could be bent in a direction in which the work piece is concave toward the laser beam. That is, in the bending method in which a work piece is bent by a difference in stresses within the work piece caused by heating by laser beam irradiation and cooling, the laser irradiated side (front surface) of the work piece has a larger contraction than the backside of the work piece during a process in which a portion of the laser irradiated side is rapidly heated and then rapidly cooled. For this reason, it has been thought that the work piece is bent in the direction in which the work piece is concave toward the laser beam. Therefore, it has been thought that a work piece cannot be bent in a direction in which the work piece is convex toward the laser beam.
Thus, when a work piece is needed to be bent in opposite directions, a laser beam is irradiated on both the front and back surfaces of the work piece. That is, an individual laser irradiation head is provided on each of the front and back sides of the work piece, or a mechanism for turning the work piece is provided. As mentioned above, when the work piece is required to be bent in opposite directions, a structure of the laser bending machine becomes complex, and a manufacturing cost of the laser bending machine is increased.
Among many work pieces, there is a case in which a coil or a mold part is previously formed on one side of the work piece such as a component part use as a contact of a relay. In such a work piece, since a laser beam cannot be irradiated from a backside of the work piece, bending is limited to only one direction. Therefore, it is difficult for the conventional laser bending machine to bend a work piece in opposite directions, and there is a problem in that if an amount of bending is in excess, a correction cannot be carried out by bending in opposite directions.
For example, there is a case in which a laser bending method is used for adjusting or correcting a roll angle or a pitch angle of a suspension which elastically supports a magnetic head. In this case, each of the roll angle and the pitch angle can be adjusted by irradiation of a laser beam in one direction. However, there is a problem in that an end position of the suspension is shifted due to the laser beam irradiation in one direction, and it is difficult to adjust the roll and pitch angles while maintaining accurate dimensions of the suspension. Moreover, a suspension for a magnetic head is provided with a signal transmission conductive pattern on a backside thereof, and, thus, there is a problem in that a laser beam cannot be irradiated onto the backside and bending can be carried out only in one direction.
It is a general object of the present invention to provide an improved and useful laser bending method and apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a laser bending method and apparatus which can bend a work piece in opposite directions by irradiating a laser beam onto one side of the work piece.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a laser bending method of a metal plate, comprising the steps of: applying tension anneal to the metal plate; and bending the metal plate by irradiating a defocused laser beam onto a front surface of the tension-annealed metal plate so that the metal plate is bent in a state in which the front surface of the metal plate is convex at a position where the laser beam is scanned.
Additionally, there is provided according to another aspect of the present invention a laser bending apparatus for a metal plate, comprising: a laser oscillator; an optical system converging a laser beam from the laser oscillator and irradiating the laser beam onto the metal plate; a focus control mechanism controlling a focus of the laser beam so that the laser beam converged by the optical system is irradiated onto a front surface of the metal plate in a defocused state; a work support mechanism supporting the metal plate by supporting a portion of the metal plate other than a laser-irradiated portion on which the laser beam is irradiated in a state in which the laser-irradiated portion is floated in air; and a scan mechanism moving at least one of the optical system and the work support mechanism so as to scan the laser beam on the front surface of the metal plate.
According to the present invention, by irradiating laser beam onto the metal plate in a predetermined defocused state, the tension-annealed metal plate can be bent in a state where the metal plate is convex toward the irradiated laser beam. Therefore, bending in both a normal direction and a reverse direction can be achieved by irradiating the laser beam onto the front surface of the metal plate without irradiating the laser beam on the back surface of the metal plate. Thereby, a laser bending apparatus for bending a work piece in the normal and reverse directions can be made with a simple structure. Additionally, a laser bending apparatus, which has been conventionally used for bending a work piece in one direction, can be changed to a laser bending apparatus for bending a work piece in the normal and reverse directions with a simple modification. Moreover, even if the laser irradiation on the back surface is difficult, desired bending can be carried out by merely irradiating the laser beam on the front surface of the work piece.
In the present invention, the laser beam may be irradiated onto the metal plate while a portion to be irradiated by the laser beam is floated in air by supporting a part of the metal plate other than the portion to be irradiated by the laser. Additionally, a temperature of the metal plate may be controlled by a gas having a predetermined temperature being brought into contact with a back surface opposite to the front surface of the metal plate. The gas may be a hot air heated at the predetermined temperature, and the hot air may be blown toward the back surface of the metal plate. Alternatively, the gas may be a cold air cooled at the predetermined temperature, and the cold air may be blown toward the back surface of the metal plate.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.